A switching device is an electrical component that can break an electrical circuit, interrupting the current or diverting it from one conductor to another. A switching device may include semiconductor devices such as bipolar junction transistors or field-effect transistors and a number of terminals. When a control signal is applied to the switching device, it may open and/or close. When the switching device is closed, a small residual resistance may remain between the number of terminals.
Memory devices are typically provided as internal, semiconductor, integrated circuits in computers or other electronic devices. There are many different types of memory, including random-access memory (RAM), read only memory (ROM), dynamic random memory (DRAM), synchronous dynamic random access memory (SDRAM), flash memory, and resistive, e.g., resistance variable, memory, among others. Types of resistive memory include programmable conductor memory, phase change random access memory (PCRAM), and resistive random access memory (RRAM), among others.
Memory devices are utilized as non-volatile memory for a wide range of electronic applications in need of high memory densities, high reliability, and low power consumption. Non-volatile memory may be used in, for example, personal computers, portable memory sticks, solid state drives (SSDs), digital cameras, cellular telephones, portable music players such as MP3 players, movie players, and other electronic devices.
Memory devices may include a number of memory cells arranged in a matrix, e.g., array. A resistive memory cell can comprise a resistive storage element and a select device. As an example a select device can be a diode, a field effect transistor (FET), or bipolar junction transistor (BJT), among other switching devices used to select, e.g., access, a memory cell. The select device of a memory cell can be coupled to, for example, an access line, e.g., word line, forming a “row” of the array. The storage elements of each memory cell may be coupled to a data/sense line, e.g., bit line, in a “column” of the array. In this manner, the select of a memory cell may be accessed through a row decoder activating a row of memory cells by selecting the word line coupled to their gates. The programmed state of a row of selected memory cells may be determined, e.g., sensed, by causing different currents to flow in the memory elements depending on the resistance associated with a programmed state of a selected memory cell.
Memory cells may be programmed, e.g., written, to a desired state. That is, one of a number of programmed states, e.g., resistance levels, can be set for a memory cell. For example, a single level cell (SLC) can represent one of two logic states, e.g., 1 or 0. Resistive memory cells can also be programmed to one of more than two programmed states, such as to represent more than two binary digits, e.g., 1111, 0111, 0011, 1011, 1001, 0001, 0101, 1101, 1100, 0100, 0000, 1000, 1010, 0010, 0110, or 1110. Such cells may be referred to as multi state memory cells, multi-digit cells, or multilevel cells (MLCs).